Isoprenoids are compounds derived from the five-carbon molecule, isopentenyl pyrophosphate. Investigators have identified over 29,000 individual isoprenoid compounds, with new ones continuously being discovered. Isoprenoids are often isolated from natural products, such as plants and microorganisms, which use isopentenyl pyrophosphate as a basic building block to form relatively complex structures. Vital to living organisms, isoprenoids serve to maintain cellular fluidity and electron transport, as well as function as natural pesticides, to name just a few of their roles in vivo. Furthermore, the pharmaceutical and chemical communities use isoprenoids as pharmaceuticals, nutraceuticals, flavoring agents, and agricultural pest control agents. Given their importance in biological systems and usefulness in a broad range of applications, isoprenoids have been the focus of much attention by scientists.
Conventional means for obtaining isoprenoids include extraction from biological materials (e.g., plants, microbes, and animals) and partial or total organic synthesis in the laboratory. Such means, however, have generally proven to be unsatisfactory. For example, organic synthesis is usually complex since several steps are required to obtain the desired product. Furthermore, these steps often involve the use of toxic solvents, which require special handling and disposal. Extraction of isoprenoids from biological materials may also require toxic solvents. In addition, extraction and purification methods usually provide a low yield of the desired isoprenoid, as biological materials typically contain only small quantities of these compounds. Unfortunately, the difficulty involved in obtaining relatively large amounts of isoprenoids has limited their practical use. In fact, the lack of readily available methods by which to obtain certain isoprenoids has slowed down the progression of drug candidates through clinical trials. Furthermore, once an isoprenoid drug candidate has passed the usual regulatory scrutiny, the actual synthesis of the isoprenoid drug may not lend itself to a commercial scale.
As a solution to such problems, researchers have looked to biosynthetic production of isoprenoids. Some success has been obtained in the identification and cloning of the genes involved in isoprenoid biosynthesis. For example, U.S. Pat. No. 6,291,745 to Meyer et al. describes the production of limonene and other metabolites in plants. Although many of the genes involved in isoprenoid biosynthesis may be expressed in functional form in Escherichia coli and other microorganisms, yields remain relatively low as a result of minimal amounts of precursors, namely isopentenyl pyrophosphate.
In an effort to address the lack of isopentenyl pyrophosphate, some investigators have attempted to increase isopentenyl pyrophosphate production. Croteau et al. describe in U.S. Pat. No. 6,190,895 the nucleic acid sequences that code for the expression of 1-deoxyxylulose-5-phosphate synthase, an enzyme used in one biological pathway for the synthesis of isopentenyl pyrophosphate. Low yields of isopentenyl pyrophosphate remain, however, since several more enzymes are needed to catalyze other steps in this isopentenyl pyrophosphate biosynthetic pathway. Further, the reference does not address an alternative pathway for isopentenyl pyrophosphate biosynthesis, namely the mevalonate pathway.
Thus, the current invention is directed toward solving these and other disadvantages in the art by increasing the typically low yields associated with conventional synthesis of isopentenyl pyrophosphate and isoprenoids. Specifically, the current invention is directed toward identification of new methods for the synthesis of isopentenyl pyrophosphate, as isopentenyl pyrophosphate represents the universal precursor to isoprenoid synthesis.